Water Equivalent
It is the quantity of water whose thermal capacity is same as the heat capacity of the body. It is denoted by W.
W = ms = heat capacity of the body.
Latent Heat The heat energy absorbed or released at constant temperature per unit mass for change of state is called latent heat. Heat energy absorbed or released during change of state is given by
Q = mL where m = mass of the substance and L = latent heat. Its unit is cal / g or J / kg and its dimension is [ L 2 T-2 ].
For water at its normal boiling point or condensation temperature( 100 ° C), the latent heat of vaporisation is
L = 540 cal / g = 40.8 kJ / mol
= 2260 kJ / kg
For water at its normal freezing temperature or melting point( 0 ° C), the latent heat of fusion is
L = 80 cal / g = 60 kJ / mol = 336 kJ / kg
It is more painful to get burnt by steam rather than by boiling was 100 ° C gets converted to water at 100 ° C, then it gives out 536 heat. So, it is clear that steam at 100 ° C has more heat than wat 100 ° C( i. e., boiling of water).
After snow falls, the temperature of the atmosphere becomes very This is because the snow absorbs the heat from the atmosphere to down. So, in the mountains, when snow falls, one does not feel too but when ice melts, he feels too cold.
There is more shivering effect of ice cream on teeth as compare that of water( obtained from ice). This is because when ice cream down, it absorbs large amount of heat from teeth.
Melting Conversion of solid into liquid state at constant temperature is melting.